Photosensitive silver halide emulsions are known in the art wherein the silver halide grains of said emulsions possess a core of silver halide having a first composition and an overcoat or shell of silver halide with a different composition. Such emulsions are known in the art as core-shell emulsions. One example of such a core-shell emulsion is found in U.S. Pat. No. 3,317,322 issued May 7, 1967 wherein the grains are described as comprising a central core of chemically sensitized silver halide and an outer shell of silver halide which is chemically sensitized subsequent to the formation of the outer shell. Other such core-shell emulsions are disclosed in U.S. Pat. No. 3,206,313 issued Sept. 14, 1965 and British Pat. No. 1,027,146 published Apr. 27, 1966.
The art has also searched for methods of providing photographic emulsions with a reduced silver content. Scarcity and expense of silver, which is one of the components of the photosensitive silver halide, makes reduced consumption of silver halide in photographic products extremely desirable.
U.K. Patent Application No. GB 2,063,499, published June 3, 1981, is directed to a photographic emulsion containing composite crystals of silver halide and copper halide or a solid solution crystal of copper halide and silver halide. The host crystal of copper halide or solid solution crystal of copper halide and silver halide is of the zinc blend type of crystal structure. The composite crystals may be prepared by adding an aqueous solution of a water-soluble halide and a silver salt solution to copper halide crystals so that silver halide is deposited through epitaxial junction on the copper halide or solid solution in the copper halide.
J. Phys. Chem. 35, 2005 (1931) discloses the growth of crystals on a substrate. Among the substances employed were those having a rock salt habit, such as sodium chloride and potassium chloride. Silver chloride is also disclosed as one of the crystals being grown on the substrate. The substrates disclosed are sheet crystals and the system employed in growing the crystals is aqueous.
The art has also disclosed the formation of AgCl single crystals on NaCl crystal bars by melting silver chloride and dipping the sodium chloride bar in the melt. This method is disclosed in Journal of Crystal Growth 41, 1977, 172-174.
The formation of crystals of AgI by condensing AgI in a vacuum chamber on a sheet substrate is described in Journal of Crystal Growth 7 (1970) 109-112. Among the substrates disclosed is sodium chloride.
U.S. Pat. No. 3,859,952, issued Dec. 17, 1974 is directed to silver halide deposited or absorbed on colloidal particles of a hydrous oxide of an element selected from the group consisting of Be, Mg, Ti, Zr, V, Cr, Mo, Fe, Mn, W, Co, Ni, Cu, Zn, Cd, Hg, Al, In, Si, Ge, Sn, Th and mixtures thereof. The method comprises mixing aqueous solutions of silver nitrate and a halide with insoluble hydrous oxide particles.